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<a name="boost.apply_visitor"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Function apply_visitor</span></h2>
<p>boost::apply_visitor &#8212; Allows compile-time checked type-safe application of the
        given visitor to the content of the given variant, ensuring that all
        types are handled by the visitor.</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../variant/reference.html#header.boost.variant.apply_visitor_hpp" title="Header &lt;boost/variant/apply_visitor.hpp&gt;">boost/variant/apply_visitor.hpp</a>&gt;

</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Visitor<span class="special">,</span> <span class="keyword">typename</span> Variant<span class="special">&gt;</span> 
  <span class="keyword">typename</span> <span class="identifier">Visitor</span><span class="special">::</span><span class="identifier">result_type</span> 
  <span class="identifier">apply_visitor</span><span class="special">(</span><span class="identifier">Visitor</span> <span class="special">&amp;</span> visitor<span class="special">,</span> <span class="identifier">Variant</span> <span class="special">&amp;</span> operand<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Visitor<span class="special">,</span> <span class="keyword">typename</span> Variant<span class="special">&gt;</span> 
  <span class="keyword">typename</span> <span class="identifier">Visitor</span><span class="special">::</span><span class="identifier">result_type</span> 
  <span class="identifier">apply_visitor</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Visitor</span> <span class="special">&amp;</span> visitor<span class="special">,</span> <span class="identifier">Variant</span> <span class="special">&amp;</span> operand<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> BinaryVisitor<span class="special">,</span> <span class="keyword">typename</span> Variant1<span class="special">,</span> <span class="keyword">typename</span> Variant2<span class="special">&gt;</span> 
  <span class="keyword">typename</span> <span class="identifier">BinaryVisitor</span><span class="special">::</span><span class="identifier">result_type</span> 
  <span class="identifier">apply_visitor</span><span class="special">(</span><span class="identifier">BinaryVisitor</span> <span class="special">&amp;</span> visitor<span class="special">,</span> <span class="identifier">Variant1</span> <span class="special">&amp;</span> operand1<span class="special">,</span> 
                <span class="identifier">Variant2</span> <span class="special">&amp;</span> operand2<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> BinaryVisitor<span class="special">,</span> <span class="keyword">typename</span> Variant1<span class="special">,</span> <span class="keyword">typename</span> Variant2<span class="special">&gt;</span> 
  <span class="keyword">typename</span> <span class="identifier">BinaryVisitor</span><span class="special">::</span><span class="identifier">result_type</span> 
  <span class="identifier">apply_visitor</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">BinaryVisitor</span> <span class="special">&amp;</span> visitor<span class="special">,</span> <span class="identifier">Variant1</span> <span class="special">&amp;</span> operand1<span class="special">,</span> 
                <span class="identifier">Variant2</span> <span class="special">&amp;</span> operand2<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Visitor<span class="special">&gt;</span> 
  <a class="link" href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">apply_visitor_delayed_t</a><span class="special">&lt;</span><span class="identifier">Visitor</span><span class="special">&gt;</span> <span class="identifier">apply_visitor</span><span class="special">(</span><span class="identifier">Visitor</span> <span class="special">&amp;</span> visitor<span class="special">)</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp200626944"></a><h2>Description</h2>
<p>The behavior of <code class="computeroutput">apply_visitor</code> is dependent on
        the number of arguments on which it operates (i.e., other than the
        visitor). The function behaves as follows:

          <div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">Overloads accepting one operand invoke the unary function
              call operator of the given visitor on the content of the given
              <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code> operand.</li>
<li class="listitem">Overloads accepting two operands invoke the binary
              function call operator of the given visitor on the content of
              the given <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code>
              operands.</li>
<li class="listitem">The overload accepting only a visitor returns a
              <code class="computeroutput"><a class="link" href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">generic function object</a></code>
              that accepts either one or two arguments and invokes
              <code class="computeroutput"><a class="link" href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code> using
              these arguments and <code class="computeroutput">visitor</code>, thus behaving as
              specified above. (This behavior is particularly useful, for
              example, when one needs to operate on each element of a sequence
              of variant objects using a standard library
              algorithm.)</li>
</ul></div>

        </p>
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<td><p><span class="term">Returns:</span></p></td>
<td>The overloads acccepting operands return the result of
        applying the given visitor to the content of the given operands.
        The overload accepting only a visitor return a function object, thus
        delaying application of the visitor to any operands.</td>
</tr>
<tr>
<td><p><span class="term">Requires:</span></p></td>
<td>The given visitor must fulfill the
        <a class="link" href="../variant/reference.html#variant.concepts.static-visitor" title="StaticVisitor"><span class="emphasis"><em>StaticVisitor</em></span></a>
        concept requirements with respect to each of the bounded types of the
        given <code class="computeroutput">variant</code>.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>The overloads accepting operands throw only if the given
        visitor throws when applied. The overload accepting only a visitor
        will not throw. (Note, however, that the returned
        <a class="link" href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">function object</a>
        may throw when invoked.)</td>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2002, 2003 Eric Friedman, Itay Maman<p>Distributed under the Boost Software License, Version 1.0.
    (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at 
    <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
    </p>
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